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Air Flow Over GU Bonnet Into Air Scoop


geeyoutoo
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There is a thread on Patrol 4x4 re this that has some interesting things going on. I did this test some years ago before bonnet mounted cams. Having just replaced my bonnet protector, this new one has a more aggressive upsweep so decided to do the test again inspired by the OP (Isha) from Patrol 4x4 thread, now I have a Contour HD cam, so I can document it.

The test was done at 40-60-80k with a slight hold at each speed. I have always mounted the wool in the opposite direction for these tests so the effect is a little more evident.

The flow into the airscoop is quite good, there is no evidence of back pressure which would cause the wool strands directly in the mouth to lift. You may notice the wool strand in the mouth on the far side has a tendency to flip a strand outside the scoop but then it immediately returns. Curvature of the bonnet and the fact the air scoop is offset to the bonnet centre line has a tendency to force the air to the left and right of centre, so this would explain why the far side throws a strand out and the inner doesn't.

I am quite convinced the standard airscoop does its job correctly regardless of Bullbar, fishing rod holders, etc. As to whether a bigger scoop gets more air through well it should but is it enough to make a significant difference to EGT, I don't know, suffice to say that my EGT's are sometimes that low I wonder whether it is too low, have seen them at 210C at 100k cruising, that's not normal but it has happened.

Interestingly after one of my tests the wool strands in the mouth faced backwards all of a sudden, the thermo fan under the IC had just cut in.

EDIT: When I fitted my Cross Country IC I took particular care in sealing around the IC to ensure the maximum amount of air went through the IC and not around it.

Edited by geeyoutoo
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I tend to agree with the view that the standard scoop is fine. Nissan would not have designed the setup such that air did not flow correctly into the scoop and the fact that Nissan designed the bullbar (but had it made by ARB) possibly reflects that thought has been put into this aspect as well. As far as EGTs are concerned, I think that is more to do with the air/fuel ratios under various driving conditions. A good intercooler will provide cooler and therefore denser air, but if additional fuel can't be added to make use of this, then it's pretty much a moot point.

Cheers

Ray

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The thing the majority of people overlook with things like this is the important bit is not the airflow going into the scoop or Wether there are bullbar etc a foot or 2 in front, the important bit is what is on the OTHER side of the IC.

In order for air to flow through the IC, it must be lower pressure on one side than the other. Given a low pressure side, the air will come from above or behind if it has to, it just wants to rush to the area of the lower pressure.

A radiator fan for instance does not " Suck" air as most people think, It creates an area of low pressure and the air tries to flow to that area to balance the difference.

The best way to get air thorough the IC ( without a fan and to a degree with one) would be to fit an undertray from the front of the radiator support panel back to the diff or somewhere in that area. If this was relatively sealed and has a good lip on the trailing edge to create an area of low pressure from the forward movement of the vehicle, Cooling performance of the IC and the radiator would be improved.

What you don't want is air hitting various component as the vehicle moves along and being pushed up under the bonnet increasing the air pressure under there. Even something like a simple "Bib" that was made from rubber belting that hung from under the radiator support panel and pushed the air out of the way and speed to create a negative pressure area behind it and under the bonnet would help.

You could mount a scoop 2 ft High right across the bonnet but if the pressure of the air on the underside is equal or the area for that air to travel through is on 1/10th the size of the area imposing into the airflow, You are still going to get jack flow.

A maghelic air pressure meter would be a great help in doing this sort or testing so the pressure differential under the IC/ bonnet could be compared to the pressure in or at the mouth of the scoop.

I think there may be a lot more gains to be had by looking at the airflow ( which would be hot and expanded) under the IC and where it's going that fixating on the scoop and what is on top of the IC.

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Pressure differential is important with regards to how much of the incoming air is able to pass through the intercooler and much of that is dependent on intercooler design and things that may interfere or enhance airflow underneath the intercooler. But it's equally important that air flowing into the scoop is clearly in a high pressure zone, for if it was a low pressure zone, even taking out the intercooler wouldn't have much air flowing through the scoop. Both aspects need to be factored into the equation when considering the performance of the scoop and intercooler. The demonstration shows that the scoop inlet is in fact a high pressure zone. I also wonder whether a bigger scoop is all that effective, as the current scoop may act as a better venturi, thus assisting airflow, compared to a larger scoop.

Cheers

Ray

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I tend to agree with the view that the standard scoop is fine. Nissan would not have designed the setup such that air did not flow correctly into the scoop and the fact that Nissan designed the bullbar (but had it made by ARB) possibly reflects that thought has been put into this aspect as well. As far as EGTs are concerned, I think that is more to do with the air/fuel ratios under various driving conditions. A good intercooler will provide cooler and therefore denser air, but if additional fuel can't be added to make use of this, then it's pretty much a moot point.

Cheers

Ray

Ray, do you have the info that Nissan has designed the bull bar and contracted the manufacturing of it to ARB on good authority or have a proof?

TBH I found incredibly hard to believe. Knowing a little about how various manufacturer implement local changes or and content on the vehicles my take would be that if anything Nissan Australia specified visual/esthetic profile of it and than let ARB handle the rest. So NO wind tunnel testing in Japan or even here at Monash Uni. Chances are that existing rules/regulations standards were applied and just the visual changes made to distinguish the bar from other b/bars on the market. Its all about branding. Nissan Japan was unlikely involved and indeed why would they even bother for such small/single market like Australia.

Standard scoop is probably enough to be bare minimum as I'm sure by now everyone knows that makers of mass produced cars don't built them to any higher standard than bare minimum to be sold. Perhaps niche/specialist makers do but that's it.

Just have a look at the latest Toyo Hilux scoop. It has been enlarged(widened) somewhat but it is evident its only purpose was just cosmetic as the intercooler is still the same size as before (narrow) and the flimsy channel directing the flow on the intercooler is next to useless. Its blowing air on to intercooler plastic cover :huh:

Cheers

Edited by Rumcajs
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ARB told me that once when I was there getting suspension and dual battery installed and the alloy bar was made by another company (but note that I said possibly regarding the airflow, other aspects certainly came into its design, such as airbag compliance). Nissan is now looking at manufacturing their own accessories in Australia: http://www.goauto.com.au/mellor/mellor.nsf/story2/326F8E0260742EB5CA25785600231835.

I've provided at least some anecdotal eveidence regarding my claims, sweeping statements like ...'everyone knows...' is hardly eveidence, but sure grabs at the emotions.

Cheers

Ray

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ARB told me that once .......................

I've provided at least some anecdotal eveidence regarding my claims, sweeping statements like ...'everyone knows...' is hardly eveidence, but sure grabs at the emotions......................

Cheers

Ray

I'm so sorry Ray you felt a bit emotional, like I've burst your bubble or something but your anecdotal evidence is perhaps same as mine "everyone knows" sweeping statement.

Evidence of my statement is/could be in the cars we drive because if they were designed and built to more than bare minimum than we wouldn't need to mod make changes/improve our cars would we! Like the closed crankcase ventilation debacle. Like endless warped disc on Commodores before they increased their thickness, like the auto trans cooler lines with not one but two hose clamps before being forced to make proper crimped hose/pipes assemblies and recall entire production of said units. This list goes on. My "sweeping statements" comes from daily dealings with this "bare minimum" design crap, so I'd love to tell more but I'm being muzzled by NDA. Anyway back on the topic.......Also I have seen how a bull bar designed in conjunction with aerodynamics and manufacturer input looks like. Just one off as the cost of producing it outweighs the economics being able to sell it.

While geeyoutoo's and Isha's tests are very interesting in regards to airflow directly over bonnet the fundamental questions remain, how effective is the airflow through the scoop and what effects of its shape makes on overall engine performance? Unfortunately there is just too much effort to solve/attempt to answer those properly I suppose. Kudos to above individuals for tackling the issue. I'm sure a few of us are watching with interest.

I wish I had a time and resources to take a closer look.......

Cheers

PS: That link seems to be over a year old so did it actually start or was it just the intent and got nowhere.

Edited by Rumcajs
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No bubbles burst whatsoever. I provided what ARB told me, no proof available to support that, so it's anecdotal evidence. 'Everyone knows' is like common sense, it's not all that common in reality.

Manufacturers certainly have to design and build vehicles so that they make the most efficient use of resources, but that doesn't mean corners are constantly cut. Issues that arise from time to time with new vehicles are often a simple design mistake or manufacturing problem. Mistakes happen, as there is always the human element involved. If Nissan, for example, were made to the absolute cheapest option possible, then why make the mechanicals so strong, why not just use smaller components such as for the diffs?

Your sweeping statement implies that motor manufacturers don't care about quality, durabilty etc one bit and I think that is a gross misrepresetation of the truth. Some certainly fail to meet these parameters from time time and pay dearly as a result, vis a vis, the Ford Capri and even Nissan with the early 3.0lt.

It's amazing how it seems that I'm always the one who needs to provide comprehensive evidence in debates, when those challenging me just fire examples off the cuff.

Cheers

Ray

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The demonstration shows that the scoop inlet is in fact a high pressure zone. I also wonder whether a bigger scoop is all that effective, as the current scoop may act as a better venturi, thus assisting airflow, compared to a larger scoop.

No, the wool demonstration shown air flow, not air pressure. It says nothing about the pressure zone of the air or the pressure into the scoop . Only that can be shown with a differential air pressure meter as I mentioned. I have in fact serious doubt about the scoop being in a high pressure area going on gut feeling and experience with playing with this stuff.

Firstly it's too low and would be picking up a lot of disturbed boundary layer air which on a hot day would also be warmed by the bonnet. secondly the thing is sited too fat forward to be in a high pressure area. There is nothing around it to basically cause an interference to the air stream and the air to bank up which is what creates an actual high pressure area rather than an area of airflow.

There are some other vids of GU's with wool that show the direction of the air coming off to the side of the bonnet further back which is an indicator of where the high pressure area is likely to be.

On these vids it can be clearly seen that this area starts behind where the scoop finishes.

Typically you find high pressure areas around headlights, air dams, bumpers, in front of windscreens, to the side of windscreens etc. YOu do not find them in areas where there is nothing to impede the airflow. In the case of this scoop I suggest it is too far forward to be in an actual high pressure area, at least at any speed that vehicle is going to be travelling at.

I'd be happy to be proven wrong though with a test done with the right and not all that expensive piece of test equipment.

As far as Nissan testing may go, I'm afraid I'm highly unconvinced of that as far as optimal location and efficency go. I'll bet they tested the thing to work to meet whatever numbers they wanted but beyond that, they don't spend any more money than they have to.

Factory spec vehicles especially of the non performance type are built to a whole load of design criteria, few of which are concerned with efficiency.

Things like meeting regulations at the lowest possible production cost are the main one.

If the things were built for may performance you wouldn't have or want to fit a larger exhaust for instance or put a fan under your IC ofr fit a better one because the maker would have already fitted components that gave the best results.

Obviously that's not what they do.

I agree totally with the Bare Minimum crap. It's all done as cheap as possible.

People bag Harleys but The build quality and integrity on those things leaves any vehicle I have worked on for dead. They use hex head and normal bolts that are made from real steel not a steel and Butter alloy that strips as soon as you apply some decent torque. They may be heavy as hell but that's because they put the material in the parts so they don't fail and they do last. 100,000 KM + on a Harley is nothing. On a japper it's time for the second rebuild. Yes they are different purposed machines however, the fact remains one is built to last and the other is not.

And They DO test the bikes and the accessories properly.

Nothing Harley is cheap but you know when you hold it you are getting a quality part unlike with Nissan where you know you just got screwed for a $30 plastic POS sun visor clip ETC.

As for the efficiency of the scoop and IC, all you would have to do there is measure the in and out temps of the IC and test different scoops or try wind-age trays mocked up out of cardboard or rigid plastic sheet and see what made a difference.

I reckon just putting a raised lip or an overlying extension on the top edge of the scoop in something like pool noodle foam would make a difference straight off.

I'll guarantee it wouldn't take much at all to improve what's already there.

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It does show air pressure effects on the wool. The air vent at the base of the windscreen is a high air pressure zone, which allows air to flow into the vehicle through the internal vents. If it were a low air pressure zone, you'd get no air coming in unaided. A similar effect is occuring at the scoop inlet. Fortuitously enough here's an article explaining exactly that (always having to produce the evidence):

http://autospeed.com.au/cms/title_Undertrays-Spoiler-Bonnet-Vents-Part-3/A_2162/article.html

I'm afraid what one thinks manufactures do and what they actually do are two entirely different things. Manufacturers will naturally build products to an acceptable performance standard and these are linked to production efficiencies, cost, design implications etc; no car that comes off a mass production line is going to be the same as a formula one race car that's effectively hand built. Some reason and reasonableness has to be applied to this type of debate. But to suggest that vehicle manufacturers don't give a fat rats arse about engineering design and efficiency of their vehicles beggars belief.

I could add a link to a Nissan website that provides info on its design activities, which probably is much the same as what all the others do, but I'm sure that it would be received with much derision, so no point in creating additional waves.

Cheers

Ray

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You don't seem to be having a good day today Ray.

I'm not trying to argue with you personaly, only debate and clarify the physics and science.

The article you linked to is very clear in demonstrating that the air pressures were tested with a meter, not wool. On the example Pic and attached chart, it also clearly shows that the location where the Nissan scoop is located is far from an ideal position and not in a high pressure area at all.

It's in a Positive pressure area but not in a particularly high one.

Leading Edge of Bonnet

Front Third of Bonnet

Midpoint of Bonnet

Rear of Bonnet

Above bonnet pressure

-0.5

-0.3

0.1

+0.6

Below bonnet pressure

0.1

0.1

0.3

0.4

Difference

0.6

0.4

0.2

-0.2

2162_7lo.jpg

As for the rest, well I'll leave it at that because you seem to be reading into things that were never said or implied and I don't want to cause any ill feelings.

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I'm having a very good day, more assumptions debunked. :D

Yes, the article was more advanced in it's testing processes, which is why I provided it. That said, the article clearly indicates that the area where the Patrol scoop approx sits is a higher pressure area, but one can't take the figures shown to be directly comparable, due to differences in bonnet design, vehicle design etc. Additionally, that scoop is not a factory scoop, the owner has placed it there as described in an older article (you can clearly see in the very first photo that it's not a factory scoop and it's actually a scoop for the airbox, not intercooler). But you have once again assumed that Nissan has failed to properly engineer a product, now that's not having a very good day. ;)

Cheers

Ray

Edited by Ray!
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Firstly, if the IC Scoop was in a High Pressure zone it would bloody well fill up with leaves and other rubbish, in the 12 years I have owned mine I honestly can't remember the last time I pulled a leaf from the IC.

On a recent trip to SA a leaf came down on the vehicle while I was sitting on 100k, the leak folded over the top of the scoop and slid from side to side during cornering until it unhooked it self and blew over the top. I watched this with interest for several minutes trying to analyse what was happening, and I think the proof was there, as I've always put forward the scoop is on the periphery of the high pressure zone, allowing it to collect cool air but not the garbage that can be in it. Whether this is planned or accidental does not matter one iota.

From my vid above you will see there is no evidence of spill or back pressure, what air goes in is getting away very cleanly. During high summer I did a test on mine where I measured the inlet temp and exit temp and I found 10C differential with my Cross Country, from memory the ambient was 38C that day. So to me the argument becomes academic, it works, whether you have bullbar/fishing rod holders/Driving lights or a partridge in a pear tree.

Also note there is a difference in shape between the early GU's and the later CRD bonnets, there is a crease depression about 120mm in front of the scoop, this may change the reaction between the two, but I would not think it too significant.

Edited by geeyoutoo
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I clean stuff like leaves, bees and gnat's knees, off the top of my intercooler all the time. Not that it gets clogged, nor does my radiator or window vents, but stuff accumulates there none the less. That kind of indicates that things are working all round.

Cheers

Ray

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